An inflatable vehicle occupant protection device, such as an air bag, is part of an apparatus which further includes a crash sensor and an inflator. The crash sensor senses vehicle conditions that indicate the occurrence of a crash. When the crash sensor senses a crash-indicating condition of at least a predetermined threshold level, the inflator is actuated. The inflator then emits inflation fluid which inflates the air bag into the vehicle occupant compartment to help restrain movement of an occupant of the vehicle.
An air bag and an inflator are typically assembled together as parts of an air bag module which is separate from the crash sensor. The air bag module is located in the vehicle adjacent to the vehicle occupant compartment. For example, a driver's side air bag module may be located on the vehicle steering column. A passenger side air bag module may be located in the vehicle instrument panel.
In addition to the air bag and the inflator, an air bag module typically includes a reaction structure, a retainer, and a cover. The reaction structure supports the inflator. The reaction structure may thus comprise, for example, a reaction canister which contains the inflator, or a reaction plate upon which the inflator is mounted. The reaction structure may alternatively comprise a structural portion of a vehicle part, such as a seat, door, or instrument panel, upon which the inflator is mounted. The retainer typically comprises a circular or rectangular ring surrounding the inflator. An edge portion of the air bag also surrounds the inflator. The edge portion of the air bag is clamped between the retainer and the reaction structure.
The cover includes a deployment door which extends over the air bag to conceal the air bag and the other parts of the module from view in the vehicle occupant compartment. When the inflation fluid emitted from the inflator begins to inflate the air bag, it moves the air bag outward against the deployment door on the cover. The cover ruptures under the force of the inflation fluid pressure acting on the air bag. The deployment door is then moved pivotally out of the path of the air bag as the inflation fluid continues to inflate the air bag outward from the cover and into the vehicle occupant compartment. In addition to rupturing the cover, the force of the inflation fluid pressure tends to pull the clamped edge portion of the air bag in a direction outward from between the retainer and the reaction structure.